1. Field of the Invention
This invention relates to a magnetic disk cartridge containing a thin, flexible, small-diameter magnetic disk which is rotated at high speed for recording and read-out of data. More particularly, with respect to magnetic disk cartridges employing a center core to support the magnetic disk for such high-speed rotation, this invention relates to an improved center core support structure.
2. Description of the Prior Art
There have heretofore been provided floppy disks consisting of a base of flexible polyester sheet or the like on both sides of which is formed a layer of magnetic material in which information is magnetically recorded by means of a magnetic head while the disk is rotated at high speed. Because they are easy to handle and are low in cost, such floppy disks are widely used as recording media for computers. These advantages of floppy disks and the ability to re-use them, which is not possible with silver-halide photographic film, has caused such floppy disks to be provided in a smaller form as the image recording media in electronic still cameras. For such cameras the disks are used in the form of a magnetic disk cartridge consisting of a casing within which is rotatably housed the disk.
Such magnetic disk cartridges are provided with a center core. The round top of the center core is exposed by an opening provided in the center of the cartridge case, and the center core has a flange portion at the lower edge of its cylindrical periphery which forms a continuity with the said top. The magnetic disk is integrally supported by the flange portion, and the top of the center core is gripped by a gripping means on an electronic still camera or the like which transmits a rotation so that the center core and magnetic disk rotate together at high speed. In order to integrally affix the magnetic disk to the flange portion, a method in general use is to employ a ring-shaped double-sided adhesive member disposed between disk and flange to thereby affix the disk and flange. More specifically, the protective paper is peeled from one side of the ring-shaped double-sided adhesive member which is then lowered down over the top of the center core, with the exposed adhesive side downwards, and brought down onto the flange for adhesion thereto. The protective paper is then removed from the other side of the double-side adhesive member and the magnetic disk is also then lowered down over the center core for adhesion, integrally fastening the disk to the flange portion. However, with the conventional core, as the flange portion has had to be perpendicular to the periphery of the core, the inner edge of the flange portion that is coterminous with the periphery curves, forming a rounded slope. Consequently, the double-side adhesive member had to be provided with sufficient dimensional tolerance relative to the core periphery to allow it to be stuck in position without forcing, but this tolerance has caused misalignment of the adhesive member, with part of it riding up on the curved portion, causing curling of the magnetic disk affixed to the top, which because of the thinness of the disk produced wrinking of the disk surface.
When rotated at high speed, a magnetic disk thus deformed undulates. In small magnetic disks with very high-density storage capability, the slightest deformation or displacement of the disk produces distortion in data recorded on or read from the disk, making it difficult to achieve good recording/read-out, and in addition, especially with double-sided magnetic disks in which data is stored on both sides, such undulations cause differences in the outputs of the magnetic read/write heads which operate in contact with the two sides of the disk. Also, when the center core is of metal which has been stamped and press-formed, in many cases the flange portion retains flashing on its lower edge, and when the center core is rotated this flashing sometimes rubs against the inside wall of the cartridge casing, scraping off fragments of the wall which stick to the surface magnetic disk, causing data dropout.